Hey Mr. Blue Tape,
I downloaded your example files onto my Kindle DX and took some photos to show you how they appear. I had to take the photos without flash with a wide aperture, so some areas of the photo are a bit soft from a narrow depth of focus. But everything on the screen is very clean and sharp. I zoomed in 200% on the column of text of the chess PDF in the second photo. The pen is beside the Kindle to show scale. The types of PDFs you would like to use appear fine on the screen. But I highly recommend you consider the DX model over the Kindle 3 as I can't imagine reading many of these documents on a smaller screen than this without a lot of zooming and panning.
Click on the thumbnails to get a larger view (use the zoom button the following page to see them as 1200x800 photos):